Alkylation process



Sept. 19, 1961 A. R. GOLDSBY ETAL 3,000,991

ALKYLATTON PROCESS Filed DSC. 7. 1959 N RNW@ nited States Patent3,000,991 ALKYLATIGN PROCESS Arthur R. Goldsby, Chappaqua, and Louis A.Clarke,

Fishkill, NX., assignors to Texaco Development Corporation, New York,N.Y., a corporation of Delaware t Filed Dec. 7, 1959, Ser. No. 857,981 3Claims. (Cl. 260-683.46)

This invention is directed to a method of reacting propylene andisoparain in the presence of an alkylation catalyst and moreparticularly to such. an alkylation process employing a clean-upreaction zone wherein a promotional amount of an alkylation promoter isintroduced With the reactants and catalyst into the clean-up reactionzone. I i

Alkylation of olefinic materials With isoparaffins is employedextensively for the production of high octane number fuels. Thealkylation reaction is effected in the liquid phase in the presence of aliquid catalyst. The alkylation reaction is directed to Vthe productionof a maximum yield of high product quality alkylate with minimumcatalyst consumption by maintaining 4desirable operating conditionsincluding conditions of intimate mixing, low temperature, and highratioof isoparafiin to olefin. Intimate contact of the reactants andcatalystis effected by intensive mixing forming an emulsion of liquidhydrocarbon and catalyst. The alkylation reaction temperature isdesirably maintained within a range of about 35 to 75 F. It is necessaryto refrigerate the reactants and reaction mixture to maintain adesirable reaction temperature since a large amount of heat is liberatedas the heat of reaction of the olefin and isoparafn. Mixing is typicallyobtained by rapid circulation of the reaction mixture by means of pumpsas in pump and tank systems or by means of impellers or jets in internalcirculating systems. Refrigeration may be provided by autorefrigeration,effluent refrigeration or external refrigeration as is Well known in theart. In all of these systems, an emulsion of the reaction mixture isformed and circulated in the reaction zone. Reactant hydrocarbons andcatalyst are continuously added to the reaction mixture, and a portionof the emulsion is continuously Withdrawn. The emulsion which isWithdrawn is separated into catalyst and hydrocarbon phases; thecatalyst phase is recycled and alkylateproduct is recovered from thehydrocarbon phase.

In the catalytic alkylation of olefins with isoparafiins, apreponderance of isoparafiin (typically about 60 to 80 volume percent ormore of the hydrocarbons in the reaction mixture) over olefin materialand hydrocarbon diluents is used to direct the reaction towardsproduction of the most valuable aviation or automotive fuels.Consequently a large quantity of isoparain must be recovered andrecycled for reuse in the process. Isobutane is generally used as theisoparaflin for the manufacture of aviation or motor fuels althoughother isoparains, for example isopentane, may be employed.

' In catalytic alkylation, the mol ratio of isoparafiin to olefin-basedmaterial supplied to the alkylation zone is maintained substantially inexcess of l to l, and preferably within the range of about 4 to l toabout 20 to l. The catalyst to liquid hydrocarbon volume ratio ismaintained within the range of about 0.5 to 1 to about 5 to 1 andpreferably within the range of about 1 to 1 to about 3 to l. Catalyststrength is maintained of at least about 88 percent when sulfuric acidis used, of at least about 85Y percent titratable acidity when hydrogenfluoride is used or of at least l5 weight percent aluminum chloride(expressed as equivalent aluminum) when `aluminum chloride-hydrocarboncomplex liquid catalyst is used. A liquid catalyst which is non-volatileunder alkylation reaction conditions, for example, sulfuric acid, ispreferred.

Sulfuric acid strength is maintained within the range of about 88 to 95percent by purging spent acid from the system and by adding make-up acidof about 98.0 to 99.9 percent purity.

An important part of the isobutane employed in alkylation processing isa recycle stream produced by fractional distillation of alkylationproducts in a deisobutanizing fractional distillation zone, theisobutane being recovered as a distillate fraction of high isobutaneconcentration, for example, about to 95 liquid volume percent isobutane.The higher-boiling alkylate in such distillation zone is recovered inthe liquid bottoms fraction. This liquid bottoms fraction may befractionated in conventional manner to separate light ends and alkylatefractions for use as fuel blending stocks. In the usual deisobutanizingfractional distillation operation, isobutane distillate is returned tothe top of the distilling column as reflux at a high reflux ratio, forexample 4 to l, to maintain high isobutane purity in the distillate.

In the alkylation reaction, it is postulated that the olefinic materialreacts With the catalyst forming an acid ester as an intermediateproduct and that this intermediate product then reacts with isoparaftinreleasing the catalyst and forming alkylate. Although the alkylationreaction is rapid and proceeds substantially to completion in `reactionsystems wherein reactants are continuously added to circulatingemulsion, the acid ester intermediate product is present in the catalystphase of the emulsion. As a result, a part of the olefin feed, forexample, up to about l0 percent of the olefin feed, may appear as theacid ester intermediate product in the emulsion phase Which is withdrawnfrom the reaction zone in prior art processes. If emulsion containingintermediate products is passed directly to a settling zone, theseintermediate products tend to react further with the catalyst byconjunct polymerization effecting degradation of the catalyst and theformation of hydrocarbons of poor fuel quality since the hydrocarbonfraction rich in isobutane is no longer in intimate contact with thebulk of the acid containing the intermediate products after coalescenceof the acid in the settler. This undesirable reaction in the settler isevidenced by a temperature rise which may be as much as 10 F. Theseintermediate products may be converted to alkylate by contact withisoparaffin in a supplemental finishing or clean-up reaction zone towhich emulsion is passed in the absence of additional olefin feed stock.In this Way, the formation of alkyl acid esters is stopped and thecontinued reaction of the ester with the isoparain substantially reducesthe ester content of the emulsion discharged from the nishing reactor.When the olefin employed in alkylation is propylene or propylene inadmixture with other olefins, for example, propylene-butylene mixtures,conversion of acid esters in the finishing reactor is incomplete and theefiiuent from the finishing reaction zone may contain about 3.0 Weightpercent propyl acid ester. In general the introduction of olefin feedstock into the finishing reaction zone would be expected to defeat thepurpose of a finishing reactor since additional intermediate products,alkyl acid esters, would be formed. However, We have found that theamount of propyl acid ester in the effluent of the finishing reactionzone may be -substantially reduced by introducing a small amount of apromoter into the finishing reaction zone. Promoters useful in thealkylation of propyl acid esters with isobutane include butylenes andlow boiling butylene polymers such as diisobutylene. Isobutylene is apreferred promoter. The promoter is used in an amount within the rangeof about 20.0 to 80.0 Weight percent of the alkyl acid ester content ofthe emulsion passed to the finishing reaction zone thereby effectivelypromoting conversion of the intermediate reaction products present inthe feed to the finishing reaction zone without introducing fresh olefinin an amount to produce additional intermediate products.

In one embodiment of our invention, the emulsion from the first reactionzone is separated into hydrocarbon and catalyst phases and only thecatalyst phase is passed with promoter and additional isoparafiin to afinishing zone. -In this case, it is preferred to effect the separationof the emulsion from the first zone by an accelerated separationtechnique, for example by centrifugation. The emulsion from thefinishing zone may be returned directly to the first reaction zone or itmay be separated into hydrocarbon and catalyst phases for separation ofthe alkylate produced.

An advantage of the process of this invention is that intermediatereaction products produced in the alkylation of propylene areefficiently converted to high quality alkylate.

Another advantage of this invention is that catalyst degradationresulting from reaction of intermediate products in the catalystseparator are avoided Another advantage of this process is that thecatalyst recycle stream before .introduction into the primary alkylationzone is preconditioned by contact with a stream of high relativeisoparaflin content as compared with other reactants and reactionproducts.

The accompanying drawing diagrammatically illustrates the process ofthis invention. Although the drawing illustrates one arrangement ofapparatus in which the process of this invention may be practiced, it isnot intended to limit the invention to the particular apparatus ormaterial described.

Referring to the drawing, a hydrocarbon feed cornprising olenic andparaflinic hydrocarbons, for example, a propylene-butylene fraction fromcatalytic cracking, is introduced through line 2 into contactor 3.Catalyst, for example, sulfuric acid, in line 4 and isobutane recyclestreams in lines 5 and 6 are also passed to contactor 3. The contents ofcontactor 3 are circulated rapidly by an impeller 7 effecting formationof an emulsion of hydrocarbon and catalyst. The emulsion circulated incontactor 3 is cooled by heat exchange coil 8. A portion of thecirculating emulsion is withdrawn through line 9, admixed with analkylation promoter, for example isobutylene, from line 10 and themixture is discharged to finishing contactor 11. Finishing contactor 11is provided with impeller 12 to maintain intimate mixing of the contentsand cooling coil 14 to maintain the reaction temperature at a desiredlevel. Iincompletely reacted olefin in the form of propyl acid esterpresent in the acid phase of the emulsion reacts with isobutane in thepresence of the promoter to form alkylate.

Efliuent from finishing contactor 11 is discharged through line 15 tosettler 16. Settler 16 is a quiescent zone wherein hydrocarbon and acidcatalyst phases separate, the lighter hydrocarbon phase rising to thetop as indicated by numeral 17 yand the heavier acid catalyst phasesettling to the bottom as indicated by numeral 18. Acid catalyst iswithdrawn through line 19 and recirculated to the contactor 6 throughline 4. Spent acid is withdrawn through line 20 and make-up acid isadded through line 21 to maintain the concentration of the acid in thesystem at a desired level.

Hydlrocarrbon liquid is withdrawn from settler 16 through line 22 andpassed through throttle valve 23 wherein the pressure is reducedeffecting concomitant vaporization of a part of the hydrocarbon andchilling of the resultant liquid-vapor mixture. The chilled liquidvapormixture is discharged through lines 24 and 25 to cooling `coils 8 and 14respectively to provide refrigeration and absorption of the heatliberated in the respective contactors. Efliuent from cooling coil 8 isdischarged through line 26, combined with the effluent from cooling coil14 in line 27 and the mixture is discharged through line 28 to vaporseparator 30. Liquid separated in separator 30 comprising productalkylate and unreacted isobutane is withdrawn through line 31 toneutralization and fractionation facility 32. Alkylate is dischargedthrough line 33 for use as high octane motor or aviation fuel. Recoveredisobutane from neutralization and fractionation facility 32 is recycledthrough line 5 to confactor 3.

Vapor from separator 30 consisting substantially of isobutane iswithdrawn through line 35 and is condensed by means of compressor 36 andcooler 37. Condensate from cooler 37 is passed through line 6 tocontactor 3.

Example In the following example flow rates are given in barrels (42gallons) of liquid per hour regardless of whether the stream is in theliquid or vapor state. All compositions are given in mol percent.

Fresh feed comprising olefin and isobutane feed streams is provided at arate of 70 barrels per hour having the following compositions:

The fresh feed is admixed with 93.7 barrels per hour of recoveredisobutane containing percent isobutane and 169 barrels per hour ofcondensate containing 77 percent isobutane and charged to primarycontactor. Ink

addition 333 ybarrels per hour of sulfuric acid catalyst is introducedinto the primary alkylation contactor. The catalyst is maintained at asulfuric acid concentration of about 90.0 percent sulfuric acid bywithdrawing used acid as necessary and adding make-up acid of 99.5percent purity. The hydrocarbon and acid are emulsiiied in the contactorand the resulting reaction mixture is maintained at a temperature of 40F. by coils immersed in the contactor. A portion of the emulsion iswithdrawn from the contactor as a stream of 669 barrels per hour and ispassed directly to a finishing contactor. The acid -phase of theemulsion contains about 0.7 weight percent propyl acid sulfate. A streamcontaining 40 mol percent isobutylene and 20.0 percent normal butyleneis passed to the finishing contactor at a rate of 5.4 barrels per hourand admixed with the contents thereof. Efliuent fro-m the finishingcontactor is discharged to a settler where catalyst separates containing0.1 weight percent propyl acid sulfate. Acid catalyst is withdrawn fromthe settler and recycled to the primary contactor. Liquid hydrocarbonfrom the settler is passed through a pressure reduction valve effectingpartial vaporization and chilling of resultant liquid and vapor and thechilled liquid vapor mixture is passed in indirect heat exchange withthe contents of the two contactors. Effluent from the cooling coils isdischarged into a liquid vapor separator from which is withdrawn 154.7barrels per hour of liquid comprising cru-de alkylate and unreactedhydrocarbons. The crude alkylate mixture is neutralized and is thenfractionated in admixture with 41.1 barrels per hour of field butanescomprising 55.9 percent normal butane and 38.0 percent isobutane toseparate 58.2 barrels per hour of alkylate, 28.3 barrels per hour ofnormal butane and 93.7 `barrels per hour of recovered isobutane which isrecycled to the alkylation contactor. Vapor from the refrigeration coilsis condensed, depropanized and auto-refrigerated to produce a recyclestream of 169 barrels per hour `of chilled isobutane condensate.

Obviously many modifications and variations of the invention ashereinbefore set forth may be made Without departing from the spirit andscope thereof and only such limitations should be imposed as areindicated in the appended claims.

We cIaim:

1. In an alkylation process wherein an olefnic feed stock comprisingpropylene is contacted with an isoparain in the presence of analkylation catalyst in a first reaction zone under alkylatingconditions, and at least a part of the effluent from said rst reactionzone is passed to a second reaction zone in the absence of additionaloleiinic feed stock comprising propylene whereby propyl acid esters nthe euent from said first reaction zone are converted to alkylate andreleased catalyst in said second reaction zone, the improvement whichcomprises introducing an alkylation promoter selected from the groupconsisting of butylene and low boiling butylene polymers into saidsecond reaction zone in an amount less than 'about 80.0 weight percentof the propyl acid ester content of the effluent from said rst reactionzone passed to said second reaction zone.

2. The process of claim 1 wherein said alkylation catalyst comprisessulfuric acid and said propyl acid ester comprises propyl acid sulfate.

3. A process for the reaction of propylene based material with anisoparain in the presence of an alkylation catalyst wherein saidpropylene based material, said isoparain and said catalyst are contactedin a primary reaction zone and at least a portion of the reactionmixture in said primary reaction is passed to a lnishing reaction zone,the improvement which comprises introducing an alkylation promoterselected from the group consist ing of butylenes and low boilingbutylene polymers into said finishing reaction zone in an amount withinthe range of about 20.0 to 80.0 Weight percent of the propyl acid estercontent of said reaction mixture passed from said primary reaction zoneto said finishing reaction zone.

References Cited in the tile of this patent UNITED STATES PATENTS2,245,038 Holm et al. June 10, `1941 2,340,412 Clarke et al. Feb. 1,1944 2,419,692 Shoemaker et al Apr. 29, 1947 2,618,669 Mrstik Nov. 18,1952

1. IN AN ALKYLATION PROCESS WHEREIN AN OLEFINIC FEED STOCK COMPRISINGPROPYLENE IS CONTACTED WITH AN ISOPARAFFIN IN THE PRESENCE OF ANALKYLATION CATALYST IN A FIRST REACTION ZONE UNDER ALKYLATINGCONDITIONS, AND AT LEAST A PART OF THE EFFLUENT FROM SAID FIRST REACTIONZONE IS PASSED TO A SECOND REACTION ZONE IN THE ABSENCE OF ADDITIONALOLEFINIC FEED STOCK COMPRISING PROPYLENE WHEREBY PROPYL ACID ESTERS INTHE EFFLUENT FROM SAID FIRST REACTION ZONE ARE CONVERTED TO ALKYLATE ANDRELEASED CATALYST IN SAID SECOND REACTION ZONE, THE IMPROVEMENT WHICHCOMPRISES INTRODUCING AN ALKYLATION PROMOTER SELECTED FROM THE GROUPCONSISTING OF BUTYLENE AND LOW BOILING BUTYLENE POLYMERS INTO SAIDSECOND REACTION ZONE IN AN AMOUNT LESS THAN ABOUT 80.0 WEIGHT PERCENT OFTHE PROPYL ACID ESTER CONTENT OF THE EFFLUENT FROM SAID FIRST REACTIONZONE PASSED TO SAID SECOND REACTION ZONE.